2010 Update

The first WG 135 Meeting took place in Woods Hole, Massachusetts, USA on 23-24 Nov. 2009. Logistical support was provided for this meeting from InterRidge, which arranged access to all meeting facilities at WHOI. The aim of this first meeting was to discuss the most relevant way to address the WG terms of reference and to clarify the expected outcomes of the WG, while discussing science plans and opportunities arising in partnership with various other initiatives.

After a general introduction of SCOR (E. Urban) and InterRidge (J. Lin), first items on the agenda were to address the links of the WG with current international initiatives.

• The multi-disciplinary input that this WG could provide to GEOTRACES (SCOR) though a Chemical Oceanography proposal for a series of submersible dives, as a complement to a planned southern East Pacific Rise GEOTRACES transects was the first such example to be mentioned.

• Potential for complementary initiatives was also identified with a number of IODP projects planned in partnership with the InterRidge Deep Earth Sampling WG and/or arising from a recent ‘Dark Energy’ (NSF-NASA) workshop, focussing on the deep (sub-seafloor) biosphere. In a related development, the Dark Energy Biosphere Institute (DEBI) has recently been funded by NSF to resolve the extent, function, dynamics, and implications for the sub-seafloor biosphere. Key themes for the forthcoming North Pond (Mid-Atlantic Ridge flank) IODP drilling project include: functions and rates of global biogeochemical processes; the extent of life in the deep biosphere; limits to the existence of life; and evolution and survival in the deep biosphere – all of which are directly relevant to the scope of this WG.

• A possible connection with the SCOR/IGBP IMBER programme was also discussed. To date, only pelagic ecosystems are being considered within the scope of IMBER, with increasing attention paid toward processes at greater depths below the air-sea interface, but not to benthic systems. Links will mostly be possible, therefore, through considerations of nutrient and organic carbon export from hydrothermal systems to the overlying water column.

3. Discussion on WG 135 Terms of Reference

Hydrothermal systems have been studied for 35 years now, but the issue of their impact on global-scale ocean biogeochemistry remains to be adequately addressed. Rather, vent ecosystems are often described as being largely independent of the rest of the biosphere, but the extent to which they are inter-connected with the photosynthetic world still needs to be assessed.One way of considering this question is to consider the service that is provided by these systems to the ocean as a whole. For example: if we removed hydrothermal systems from Earth, what would be the impact on ocean ecosystems and on carbon sequestration by the ocean?

How much carbon is exported out of vents (inorganic and organic carbon, including methane) remains largely unknown. Examples of relevant questions to this WG are: what do we know about the global export flux of methane from ridge axes? How much microbial biomass is trapped in the subseafloor, and how do the microbes that live within the crust affect the carbon balance to the ocean? Can we estimate the fraction and nature of organic carbon exported from vent sites to oceanic ecosystems? Beyond carbon, what other elements are likely to have a significant impact on ocean biogeochemistry? Recent estimates have suggested that 10-25% of all dissolved Fe in the deep ocean may be hydrothermally sourced, but how much impact do vents have on other trace metals that can also act as micronutrients – e.g. nickel, which is known to be important in enzymes? Conversely, we can also address the link between hydrothermal biogeochemical systems and the photosynthetic world by asking questions that consider the reverse order. For example: how much of the life at vents depends on a well-oxygenated ocean to function?

Our objective is to engage the broader community in our work and, concurrently, to help shape the future direction of submarine hydrothermal research. Key goals identified include:

1. To constrain the micronutrient hydrothermal fluxes and their influence on ocean productivity.

2. To assess the productivity of seafloor and subseafloor vent ecosystems and their dependence on oceanic processes

3. To estimate the extent of new DOC and POC production and export from seafloor hydrothermal systems and how these fluxes may influence deep water ecosystems.

One of the main difficulties in the above concerns how we calculate carbon fixation rates, locally, and then how we should extrapolate those values to apply them at the global scale. We have extant data in hand, although they are patchy. Studies are available: on microbial carbon fixation rates (mostly from the 1980s before microbial studies moved toward assessing diversity); macrobiological biomass production from symbiotic organisms; complexity in terms of geochemical composition; and energy budgets for released hydrothermal fluids, which may stimulate different microbiological processes. To identify what we still don’t know is likely to prove as important as establishing what we do already know, if we are to address our terms of reference. One possible approach would be to start with inverse modelling to identify which key rates are currently unknown. From this, it will be possible to plan the necessary measurements to constrain and/or estimate those rates.

Both axial and off-axis hydrothermal systems are hydrologically connected to the ocean system. Consequently, we need to identify the important parameters that need to be measured at these quite different vent systems if we are really to achieve an improved understanding of the hydrothermal fluxes that obtain across numerous different length scales. We also recognize the need to incorporate the concept of “patchiness” into our considerations and not simply generate global estimates, to ensure that we assess the role of hydrothermal circulation on ocean carbon budgets at different length scales. Global impacts usually don’t take place ‘on average’ but through localized interactions. For example, despite comprising an aerially and volumetrically insignificant component of the deep seafloor, seamounts exert a huge ecological influence as local hotspots of reproduction and diversity. Similarly, interactions with deep sea hydrothermal systems may result in bursts of productivity in deep, oligotrophic waters and, consequently, impart a profound impact on ocean carbon cycling.

New technologies– both to study large-scale processes and in the context of observatory science – are offering novel opportunities with which to further constrain geochemical and biological rates and fluxes. For example, CORK observatories in drilled holes have been used over the past 4 years to provide better access to biomass and microbial activity in the deep hard rock biosphere than is achieved from the act of drilling. Indeed, it remains difficult to recover drill-core samples of suitable quality for microbiology (or fluid chemistry) studies. A similar problem is encountered with most “snap-shot” plume studies. Measurements from one-off investigations may yield concentrations but only time-series plume investigations can be expected to yield information on hydrothermal fluxes.

One interesting point that was discussed concerns the extent to which new technology may help us to assess the “patchiness” of hydrothermal-ocean interactions in the future. Just as satellite surveys already allow us to capture global distributions of parameters in the surface ocean, next-generation AUVs such as the 6000km-range and 6000m-rated AUTOSUB already under development in the UK, when equipped with the appropriate sensors, should allow us to design new deep-ocean observation strategies, in the next 10-20 years, that are an order of magnitude more complex than anything we have been able to conduct at the deep seafloor.

4. Outcomes of the Working Group

4.1. Agenda

Some important dates over the proposed lifetime of SCOR WG135 have been identified, and these were used to inform our decision on the location and time of our second meeting.

2010

Main WG activities:

• Submission of position papers (see later).

Relevant and related activities:

• June 2010 Goldschmidt conference (Theme 5: Evolution of Oceanic Crust and its Hydrothermal Systems led by WG members Bill Seyfried and Wolfgang Bach; session in Theme 15 Geomicrobiology of Mid-Ocean Ridge Systems led by Brandy Toner)

• IR Long-Range Exploration WG community workshop in June 2010.

2011

Main WG activities:

• Second SCOR WG135 Meeting.

Xiqiu Han has offered to host the WG for its 2nd meeting at the 2nd Institute for Oceanography, in Hangzhou, China. The proposed data for the meeting is late April 2011. We might be able to anticipate some travel support from her institution (for local costs within China for board and lodging) and food.

• Submission of proposals to support a community-wide workshop (e.g. to InterRidge, ESF, AGU, other).

Relevant and related activities:

• InterRidge Mantle Imaging WG community workshop.

• Goldschmidt Conference special session (Prague, June)

2012

Main WG activities:

• Community-wide workshop (to be held in Europe, in May/June)

Relevant and related activities:

• Completion of hydrothermal GEOTRACES cruise to the Southern East Pacific Rise

4.2. Workshop date and location

The community-wide workshop for this WG will be held in Europe in May/June 2012. To sustain momentum, we will also propose related special sessions at one or more major international meetings in the interim (e.g. AGU, EGU, Goldshcmidt and and Western Pacific Geophysics meetings).

In addition to SCOR, we will seek further support from InterRidge and additional workshop funding from ESF, NSF and other national / governmental research agencies – e.g. the U. Bergen Geobiology Institute in Norway, the Sloan Foundation’s Deep Carbon program, NASA’s Astrobiology Institute and CNRS.

4.3. Position papers

Consensus was developed that two review papers should be drafted, together with a shorter paper that will capture key concepts and present them in an accessible form for a broad ocean science community, in advance of – and to set the scene for - the international community workshop in 2012. The two review papers will each start at the small length scale of a seafloor vent scale and progressively enlarge their scope and scale to answer our key questions (as summarized in Figure 1). The main goal of these papers will be to provide a basis from which to explain why we think these systems are important to study, to the broader oceanographic community, and to help establish what new approaches are needed to progress this field. Starting with the best-studied hydrothermal sites known, our framework will be to summarize existing knowledge on these three questions:

1. What are the important processes active in the system?

2. What missing information do we need to know about mechanisms and rates?

3. Where are the gaps and what new measurements are needed?

4. See Figure attached below.

Figure 1: Scheme of the approach developed for the two position papers. (2. will be synthesized in a first large review, and 1 and 3 together in a second one).

The 1st paper will focus on seafloor hydrothermal systems themselves. An integrated understanding of the processes that support these unique ecosystems should be highlighted, including considerations on both spatial and temporal scales, in as detail much as possible, and on the rates that control the magnitude and timing of input/output fluxes for nutrients and carbon between ocean and crustal “reservoirs”. Focus here will be on the extent of inorganic carbon fixation, as well as on the recycling and export of organic carbon. This paper will also need to acknowledge the importance of patchiness/spatial discontinuity, from both an ecological and biogeochemical perspective, that will then be considered in more detail in the second-tranche papers. For example, differences between diffuse versus focused flow systems and the differences imparted by changes in axial ridge topography will need to be addressed. Stefan Sievert, Julie Huber, Nadine Le Bris, and Pete Girguis will take the lead on this paper that will cover linkages between microbes, macrofauna and geochemistry and including tentative conceptual model.

The second review paper – led by Katrina Edwards, Chris German, and Wolfgang Bach –will consider the interaction with the water column and with the subseafloor. There are currently two review papers just published or in preparation partly covering this scope: Schrenk, Edwards and Huber are co-authors on a paper defining sub-seafloor provinces, subdivided into biomes, while a new review (Edwards et al), is focusing on dark ecosystems in the marine realm, to describe the pelagic regime from the base of the photic zone to the deep seafloor in terms of what we know microbiologically. Because these reviews are mostly directed toward microbiologists, we consider that a parallel paper for chemical processes at large, including chemical fluxes in environmental systems, would provide a valuable and timely complement. For example, recent work on ocean carbon budgets have focussed upon chemical reactions for photosynthesis and breakdown (decomposition) of organic matter to CO2. By contrast, this paper would bring a fundamental understanding to the attention of a wider community on the imbalance that is created through the autotrophic production of organic carbon in chemosynthetic systems with oxygen:

Reduced metal/mineral + O2 + CO2 => organic C.

Possible journals for the two longer review papers we propose include Geobiology (K. Edwards is on the editorial board), Deep Sea Research, GCA, MEPS, L&O, Annual Review and Journal of Marine Systems (L. Legendre is on the editorial board).

For the short, high-profile paper to be published first it is proposed that a journal such as Nature, Science or PNAS be approached to attract the broadest possible readership.

5. Working Group composition: complementary expertises needed

• The need to entrain someone from the JGOFS-type community to help with the large-scale review paper was raised. Philip Boyd from New Zealand was identified as one potentially ideal candidate because (i) he is well known for his expertise in open ocean iron fertilization experiments and in interests in JGOFS-like global-ocean scale C-cycling and (ii) he would provide the input/WG membership from the Southern Hemisphere that had been recommended previously but which the co-chairs had struggled to address previously. A key question that requires SCOR input is whether we could invite Boyd as an additional FULL member of the WG, or just as an associated member.

• In addition to Boyd, it was agreed that we should expand our intellectual “gene pool” by inviting three further experts to join WG 135 as Associate Members: